This invention relates to vehicle suspension systems. More particularly it relates to an anti-roll torsion bar arrangement for a vehicle suspension, wherein the anti-roll torsion bar is able to be torsionally loaded by an actuator so that, with suitable control of the actuator in response to a vehicle operating condition, roll of the vehicle can be reduced.
Examples of vehicle suspensions incorporating anti-roll torsion bar arrangements of the above types are disclosed in GB-2189751A and WO89/04262. One of the problems associated with a conventional passive anti-roll torsion bar, as has been widely used hitherto in vehicle suspensions, is that a torsion bar which is stiff enough to resist vehicle roll when cornering has a disadvantageous effect on the ride of the vehicle when it is not cornering, by restricting the ability of the vehicle suspension at opposite sides of the vehicle to operate independently. By loading the torsion bar in response to a vehicle operating condition, e.g. vehicle lateral acceleration as detected by a suitable sensor, the torsion bar can be made to resist roll when the vehicle corners without requiring the torsion bar to be so stiff as to disadvantageously affect the ride quality of the vehicle when it is not cornering. The actuator may, as disclosed in WO89/04262, load the torsion bar directly by applying a torsional input thereto at one end thereof.
One of the problems associated with such a torsion bar and actuator installation is that, if a torsion bar of low torsional stiffness (so as not to affect vehicle ride when not cornering) is to store sufficient energy effectively to resist vehicle roll during cornering, the actuator which torsionally loads the bar has to put a large torsional input into the bar. This in turn produces a problem in that high stresses in the torsion bar are generated, requiring the bar to be of a high performance, and hence expensive, material.
A further problem associated with such an anti-roll torsion bar installation is that known as "packaging", i.e. accommodating the torsion bar and associated components in the vehicle in a way which is generally convenient, taking account of factors such as the amount of space occupied by such components. At the same time, of course, there should be no disadvantage caused to the performance of the torsion bar arrangement.
Accordingly, it is the object of the present invention to provide an anti-roll torsion bar arrangement which overcomes or reduces at least one of the above mentioned problems, namely that of the required properties of the torsion bar and that of the packaging of the torsion bar arrangement.